There are three conventional rectifier topologies for low voltage applications. FIG. 1a shows the prior art forward rectifier with its main switching waveforms for steady-state operation. As shown by the waveforms in FIG. 1b, the rectifier transformer has unidirectional utilization. There is one output filter inductor, which carries full load current, leading to high current and thermal stresses for high current applications. Another problem with the prior art forward rectifier is that full load dc current bias is difficult for the inductor magnetic design and always results in bulky inductor size and hence inflexibility for PCB layout designs. As a result, the forward rectification is not suitable for high current applications.
For the center-tapped rectifier, the transformer utilization is bi-directional, however, a single output filter inductor is used to carry the whole load current. The conventional center-tapped rectifier is shown in FIG. 2a, and its key steady-state operation waveforms are shown in FIG. 2b. As shown, the transformer utilization are bi-directional, however, a single output filter inductor is utilized to carry the whole load current. Therefore, the filter inductor suffers high current and thermal stresses for high current applications, resulting in bulky inductor size and inflexibility for footprint budget and PCB layout. Moreover, the transformer secondary windings are not efficiently utilized due to the fact that one of two tapped secondary windings conducts the full load current for half of the switching period. Consequently, center-tapped rectifier is not well suited for high current applications.
FIG. 3a shows a current doubler rectifier and the corresponding key steady-state operation waveforms are shown in FIG. 3b. As shown, there are two output filter inductors, and each carries only half of the load current. Compared with center-tapped rectifier, the copper loss in the inductors is reduced and inductor magnetic design is simplified since each inductor carries half of the load current, which results in better thermal management and design flexibility. In addition, the transformer utilization is improved since the transformer secondary winding is used for bi-directional currents over the whole switching cycle and the transformer winding carries half of the load current.
In high-performance microprocessor and telecommunication applications, the system operation speed and integration density keeps increasing so that the required converter supply voltage continuously decreases while supply current continuously increases due to the increasing power level requirement. Since real estate on printed circuit boards is limited, high-current high-power-density power conversion is demanded for microprocessor and telecommunication applications. In general, conversion efficiency and thermal management are the restrictions against high power density.
High switching frequency is an effective way to improve power density, and topologies featuring high efficiency at high switching frequency are desirable. In addition, topologies with even current and thermal stresses are also demanded, especially for low voltage and high current applications. Because secondary-side conduction loss dominates the overall power loss in isolated low-voltage high-current dc-dc converters, secondary-side topologies are desirable to have low conduction loss and well-distributed power dissipation to improve overall conversion efficiency and satisfy thermal management requirement.
The present invention provides current tripler rectification topology for high current applications. Basically, an additional inductor is added in the current doubler rectifier to help share the load current, and each inductor carries only one-third of the load current. As a result, it has better power dissipation than the conventional center-tapped and current doubler topologies, leading to better thermal management and potentially improved power density. In addition, compared to center-tapped rectifier, transformer secondary winding utilization is also improved and the transformer winding conduction loss is reduced.